This invention relates to a circuit arrangement for moving a marker over the picture screen of a display device in general and more particularly to a circuit arrangement for doing this quickly and accurately.
Circuit arrangements for moving a marker having a position transmitter, upon the actuation of which pulses of switchable frequency are supplied to position counters each of which is associated with a coordinate in which the marker is displaceable, with the value stored in the counter corresponding to the position of the marker on the screen and the direction of counting controlled according to the desired displacement direction on the coordinate are known. For example, in German patent application DE-AS No. 18 17 227, filed Dec. 27, 1968 an arrangement for the marking of picture points on the screen of a television display device is described where a track (rolling) ball device, among other things, is used as a positioning unit. With such a device, a freely movable ball can be turned by hand in all directions. The rotary movements are transmitted by two friction wheels offset by 90.degree., and each associated with a coordinate of the picture screen, to signal generators, e.g., optical or magnetic pulse generators. These pulses are supplied to position counters, from which the representation of the marker is derived, so that their reading corresponds to the picture screen coordinates at which the marker is displayed.
With such a device the marker can indeed be set to every point of the picture screen, but, especially with a large number of picture points, e.g. 2048, in one line, the setting may take too long. According to DE-OS No. 24 46 692, filed Sept. 30, 1974, in which an arrangement is described by which the marker is displaced by means of keys, this problem can be solved in that, upon a short depression of a key, the marker is displaced by only one picture point. But, upon a longer key depression, the marker automatically runs in the desired direction from point to point, e.g. at intervals of 1/10 sec, and upon a longer duration of the key depression, the speed of the marker can be increased further. With this mode of marker displacement a disturbing factor is that after a key depression one must first wait for a delay time before the marker is displaced at a higher speed.
It is the object of the present invention to provide an arrangement with which a marker can be displaced on the picture screen of a display device in an ergonomically favorable manner, namely so that the displacement over large distances occurs at high speed, but yet exact positioning to a picture point is possible.